Wire bonding is a conventional method of making connections between a chip and a carrier or a chip and another chip. However, a relatively high inductance of wire bonds will lead to bandwidth limitations for the signal transmissions. Therefore, wire bonding is commonly used in a structure that transmits low-frequency signals.
Please refer to FIG. 1, which is a schematic diagram showing a connection structure 10 in the prior art. The connection structure 10 includes chips 104 and 106 and material 108, wherein the chip 104 is electrically connected to the chip 106 using a ribbon structure 102. However, in this connection mode, the two chips must be at the same height and thus the additional material 108 is usually added under the thinner chip 106 in an additional step during the manufacturing process, which causes increased cost. Although the inductance of the ribbon structure 102 is lower than that of the wire bonds, for transmissions of high-frequency and broadband signals, the operable frequency range is still limited (e.g. less than 100 GHz) due to the high inductance of the ribbon structure 102.
Please refer to FIG. 2, which is a schematic diagram showing a connection structure 20 in the prior art. The connection structure 20 includes a carrier 204, a chip 202 stacked on the carrier 204 using a flip-chip method, and a connecting unit 206, e.g. a bumper, configured on a connecting face 208 of the chip 202. The connecting unit 206 is capable of connecting the chip 202 and the carrier 204 after being heated and pressed, and via which signals between the chip 202 and the carrier 204 can be transmitted. When the connecting unit 206 is a bumper, the large size thereof will cause a severe parasitic effect, and thus the operable bandwidth of signal transmissions between the chip 202 and the carrier 204 is limited.
Please refer to FIG. 3, which is a schematic diagram showing a connection structure 30 in the prior art. In the connection structure 30, the chip and the carrier share the same substrate. The connection structure 30 includes connecting pads 301 and 302, conducting wires 303 and 304, equivalent loads 305 and 306, and wire bonds 307 and 308 connecting the connecting pad 301 to the connecting pad 302. Typically, the connecting pads 301 and 302 have a width of 200 μm, the conducting wires 303 and 304 have a length of 190 μm and a width of 100 μm, the wire bonds 307 and 308 have a width of 25 μm and a length of 32 μm, and the distance between the connecting pads 301 and 302 is about 225 μm. The equivalent loads 305 and 306 are preferably 50 ohm. In the connection structure 30, the conducting wires 303 and 304 are used as equivalent inductors, and the connecting pads 301 and 302 are used as equivalent capacitors. The microwave circuit 3012 includes the equivalent load 305, the conducting wire 303 and the connecting pad 301. The microwave circuit 3013 includes the equivalent load 306, the conducting wire 304 and the connecting pad 302. The connection structure 30 can realize a low-pass filter of orders 1 through 5 and transmit signals between two microwave circuits 3012 and 3013 via the wire bonds 307 and 308.
Unfortunately, such connection structure 30 has a large area and high cost, so it can be applied to neither signal transmission between two separate chips, nor that between an independent chip and an independent carrier. Furthermore, the connection structure 30 has the parasitic effect due to the difference between the ground potentials of the microwave circuit 3012 and 3013, and thus the bandwidth for signal transmissions is limited.
Please refer to FIG. 4, which is a schematic diagram showing a package structure 40 for transmitting signals in the THz frequency band in the prior art. The package structure 40 includes a chip 401 and a waveguide 403. The chip 401 includes a chip body 4010 and a dipole antenna 402. In the package structure 40, signals from the chip body 4010 can be radiated to the waveguide 403 via the dipole antenna 402. The waveguide 403 can be further connected to other chips or carriers to transmit signals in the THz frequency band. Although the package structure 40 has a less insertion loss, the dipole antenna 402 on the chip body 4010 usually occupies a large area and thus causes an increase in cost. Due to the large volume of the waveguide 403, which typically has a length L1 of about 1000 μm, a width W1 of about 600 μm and a height H1 of about 600 μm, the package structure 40 cannot be used to realize the miniaturized terahertz signal transmission system, and cannot be placed in handheld electronic products.
Please refer to FIG. 5, which is a schematic diagram of a transmission device 50 in the prior art. The transmission device 50 includes chips 501, 502 and 503 and spacer layers 504 and 505. The spacer layer 504 is located between chips 501 and 502, and the spacer layer 505 is located between chips 502 and 503. The chip 501 includes a transmitting circuit 5011, a receiving circuit 5012, a transmitting coil 5013 and a receiving coil 5014 on the top surface thereof as indicated in FIG. 5. Similarly, the chip 502 includes a transmitting circuit 5021, a receiving circuit 5022, a transmitting coil 5023 and a receiving coil 5024, and the chip 503 includes a transmitting circuit 5031, a receiving circuit 5032, a transmitting coil 5033 and a receiving coil 5034.
In FIG. 5, the transmitting coil 5013 and the receiving coil 5024 can convey digital signals via inductive coupling, and the digital signals are decoded in the receiving circuit 5022. However, the high attenuation of the transmission device 50 in the intensity of the transmitted digital signals is unsuitable for applications using connection structures, and due to a relatively narrow range of data transmission bandwidth, signal transmissions in the THz frequency band or millimetric wave band cannot be achieved. Because of the high signal attenuation, the amplitude of the signals output by the transmitting circuit must be large enough to allow the receiving circuit to demodulate the digital signals correctly. Based on this aspect, the transmission device 50 uses both the transmitting circuit and the receiving circuit to effectively convey signals, but this has the disadvantages of high cost and high power consumption. Furthermore, the transmission device 50 has another disadvantage, the need of thinning the chips 501, 502 and 503, and thus an additional process is required. Based on the above, the high-cost transmission device 50 is not a good choice for transmissions between a chip and a carrier or between chips.
Please refer to FIG. 6, which is a schematic diagram showing a near field communication (NFC) system 60 in the prior art. The system 60 includes resonators 601 and 602, wherein the resonator 601 includes a ring conductor 6011 and an equivalent capacitor 6012, and the resonator 602 includes a ring conductor 6021 and an equivalent capacitor 6022. The resonators 601 and 602 are separated by a distance D, which is generally at least larger than thousands of μm. Because the NFC system 60 transmits power using a near field method, the resonators 601 and 602 are required to have large quality factors, e.g. over 100, but it is hard to generate a high quality factor for the transmissions between a chip and a carrier or between chips. In addition, the NFC system 60 has a narrow operable bandwidth (tens of MHz) and a bulky size. Therefore, the NFC system 60 is not a good choice for transmissions between a chip and a carrier or between chips.
To overcome the problems mentioned above, a novel broadband connection structure and method are disclosed in the present disclosure after a lot of research, analysis and experiments by the inventors.